Mateusz Penkala

This work is the study of the role of a remote amine substituent on the terpyridine ligand in controlling the photophysical and electroluminescent behavior of complexes [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆. Introduction of the amine group into the Ph-terpy framework induced perturbations in the absorption and luminescent characteristics of [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆ relative to the parent chromophores [Ir(Ph-btz)₂(terpy-κ²N)]PF₆ and [Ir(Ph-btz)₂(C₆H₅-terpy-κ²N)]PF₆. Consistent with the presence of vibronic structure, negligible emission solvatochromism, weak rigidochromic behavior, and substantial overlap with the phosphorescence of 2-phenylbenzothiazole, the emissive triplet excited state of the model complexes was assigned to ³IL_Ph-btz with a minor ³MLCT contribution. The amine-substituted Ir(III) complexes were found to exhibit altered emission characteristics, manifested by a structureless emission band impacted by the amine group and solvent polarity. It was rationalized by a switch from the ³IL_Ph-btz/MLCT excited state in model chromophores to a configurationally mixed ³ILCT/IL/MLCT_R-terpy in [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆. With respect to the preliminary electroluminescence investigations, it was found that the introduction of the triphenylamine moiety enhances the stability of O/PEDOT/PSS/complex/Al devices. A deep insight into ground- and excited-state characters and photophysical properties of [Ir(Ph-btz)₂(R-C₆H₄-terpy-κ²N)]PF₆ was obtained by applying a wide range of experimental techniques, including cyclic voltammetry, UV-vis spectroscopy, photoluminescence spectroscopy, and transient absorption, complemented by DFT and TD-DFT calculations.

Two Ni(II) complexes containing a 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand and pseudohalide linkers ([Ni₂(bpp)₂(μ1,1-N₃)₂(N₃)₂]·2H₂O (1) and [Ni(bpp)(dca)(H₂O)]_n·n(dca) (dca – dicaynamide) (2)) show large magnetic anisotropy confirmed by HFEPR spectra (very unusual for 2) with a negative D value. The AC susceptibility reveals a field supported slow magnetic relaxation for 1 with three relaxation channels.

The impact of cyclometalating ligands on the photophysical behaviour of heteroleptic Ir( iii ) complexes with imidazo[4,5- f ][1,10]phenanthroline. [Ir(ppy) ₂ (imphen)] ⁺ is a ³ MLLCT emitter, while [Ir(pybzth) ₂ (imphen)] ⁺ has a predominant ³ LC _N∩C character.

To investigate the impact of the electron-donating morpholinyl (morph) group on the ground- and excited-state properties of two different types of Ir(III) complexes, [IrCl₃(R-C₆H₄-terpy-κ³N)] and [Ir(R-C₆H₄-terpy-κ³N)₂](PF₆)₃, the compounds [IrCl₃(morph-C₆H₄-terpy-κ³N)] (1A), 4[Ir(morph-C₆H₄-terpy-κ³N)₂](PF₆)₃ (2A), [IrCl₃(Ph-terpy-κ³N)] (1B) and [Ir(Ph-terpy-κ³N)₂](PF₆)₃ (2B) were obtained. Their photophysical properties were comprehensively investigated with the aid of static and time-resolved spectroscopic methods accompanied by theoretical DFT/TD-DFT calculations. In the case of bis-terpyridyl iridium(III) complexes, the attachment of the morpholinyl group induced dramatic changes in the absorption and emission characteristics, manifested by the appearance of a new, very strong visible absorption tailing up to 600 nm, and a significant bathochromic shift in the emission of 2A relative to the model chromophore. The emission features of 2A and 2B were found to originate from the triplet excited states of different natures: intraligand charge transfer (³ILCT) for 2A and intraligand with a small admixture of metal-to-ligand charge transfer (³IL–³MLCT) for 2B. The optical properties of the mono-terpyridyl iridium(III) complexes were less significantly impacted by the morpholinyl substituent. Based on UV–Vis absorption spectra, emission wavelengths and lifetimes in different environments, transient absorption studies, and theoretical calculations, it was demonstrated that the visible absorption and emission features of 1A are governed by singlet and triplet excited states of a mixed MLLCT-ILCT nature, with a dominant contribution of the first component, that is, metal-ligand-to-ligand charge transfer (MLLCT). The involvement of ILCT transitions was reflected by an enhancement of the molar extinction coefficients of the absorption bands of 1A in the range of 350–550 nm, and a small red shift in its emission relative to the model chromophore.

We report on the first case of the use of nonstoichiometric ternary (Ag–In–Zn–S) semiconductor nanocrystals as photoinitiators and photocatalysts of methyl methacrylate (MMA) polymerization. Two types of nanocrystals were tested, differing in their composition and characterized by red (λ_max = 731 nm) and green (λ_max = 528 nm) photoluminescence, respectively. Exploiting their reducing properties and capability of free radical generation we demonstrate that under ultraviolet (UV) radiation they effectively photoinitiate radical polymerization of MMA whereas under visible light (blue or green) they act as photocatalysts of living radical polymerization.

Photophysical properties of two Re(I) complexes [ReCl(CO)₃(R-C₆H₄-terpy-κ²N)] with remote amine groups, N-methyl-piperazinyl (1) and (2-cyanoethyl)methylamine (2), were investigated. The complexes show strong absorption in the visible region corresponding to metal-to-ligand charge transfer (¹MLCT) and intraligand-charge-transfer (¹ILCT) transitions. The energy levels of ³MLCT and ³ILCT excited-states, and thus photoluminescence properties of 1 and 2, were found to be strongly affected by the solvent polarity. Compared to the parent chromophore [ReCl(CO)₃(C₆H₅-terpy-κ²N)] (3), both designed complexes show significantly prolonged (by 1–2 orders of magnitude) phosphorescence lifetimes in acetonitrile and dimethylformamide, contrary to their lifetimes in less polar chloroform and tetrahydrofuran, which are comparable to those for 3. The femtosecond transient absorption (fsTA) measurements confirmed the interconversion between the ³MLCT and ³ILCT excited-states in polar solvents. In contrast, the emissive state of 1 and 2 in less polar environments is of predominant ³MLCT nature.

The exchange of primary hydrophobic ligands for hydrophilic ones was studied for two types of alloyed AgInS₂-ZnS nanocrystals differing in composition and by consequence exhibiting two different emission colors: red (R) and green (G). Three simple hydrophilic ligands were tested, namely, 11-mercaptoundecanoic acid, dihydrolipoic acid and cysteine. In all cases, stable aqueous colloidal dispersions were obtained. Detailed characterization of the nanocrystal surface before and after the ligand exchange by NMR spectroscopy unequivocally showed that the exchange process was the most efficient in the case of dihydrolipoic acid, leading to the complete removal of the primary ligands with a relatively small photoluminescence quantum yield drop from 68% to 40% for nanocrystals of the R type and from 48% to 28% for the G ones.

A semiconducting molecule containing a thiol anchor group, namely 2-(5-mercaptothien-2-yl)-8-(thien-2-yl)-5-hexylthieno[3,4-c]pyrrole-4,6-dione (abbreviated as D-A-D-SH), was designed, synthesized, and used as a ligand in nonstoichiometric quaternary nanocrystals of composition Ag_1.0In_3.1Zn_1.0S_4.0(S_6.1) to give an inorganic/organic hybrid. Detailed NMR studies indicate that D-A-D-SH ligands are present in two coordination spheres in the organic part of the hybrid: (i) inner in which the ligand molecules form direct bonds with the nanocrystal surface and (ii) outer in which the ligand molecules do not form direct bonds with the inorganic core. Exchange of the initial ligands (stearic acid and 1-aminooctadecane) for D-A-D-SH induces a distinct change of the photoluminescence. Efficient red luminescence of nanocrystals capped with initial ligands (λ_max = 720 nm, quantum yield = 67%) is totally quenched and green luminescence characteristic of the ligand appears (λ_max = 508 nm, quantum yield = 10%). This change of the photoluminescence mechanism can be clarified by a combination of electrochemical and spectroscopic investigations. It can be demonstrated by cyclic voltammetry that new states appear in the hybrid as a consequence of D-A-D-SH binding to the nanocrystals surface. These states are located below the nanocrystal LUMO and above its HOMO, respectively. They are concurrent to deeper donor and acceptor states governing the red luminescence. As a result, energy transfer from the nanocrystal HOMO and LUMO levels to the ligand states takes place, leading to effective quenching of the red luminescence and appearance of the green one.

To gain a better insight into the factors affecting the enhancement of the energy barrier in single molecule (single ion) magnets, three hexacoordinate cobalt(II) complexes based on the tridentate ligand 2,6-bis(pyrazol-1-yl)pyridine (pypz) and pseudohalide ions have been synthesized and investigated. It was found that dicyanoamido and azido ligands act as bridges to form a one dimensional network based on a single μ_1,5-dca bridge [Co(pypz)(dca)(H₂O]·dca (1) and dimer [Co₂(pypz)₂(μ_1,1-N₃)₂(N₃)₂]·2CH₃OH (2), while tcm⁻ counterbalanced the charge of [Co(pypz)₂]²⁺ in [Co(pypz)₂](tcm)₂ (3), where dca⁻ = dicyanamide ion; tcm⁻ = tricyanomethanide ion, respectively. The DC magnetic data show a sizable magnetic anisotropy, which was confirmed by high-field/high frequency EPR measurements. Two of them are SIMs (1 and 3) and the other one is a SMM (2). All complexes exhibit field induced slow magnetic relaxation with two (1 and 2) or three relaxation channels (3) and an exceptionally long relaxation time for the low-frequency channel upon application of an external field B_DC = 0.4, 0.3, and 0.4 T at T = 1.9 K; τ(LF) = 1.9, 2.1 and 0.9 s, respectively. Additionally, the high spin-reversal barriers, U = 103 K for 1 and 95 K for 2, are among the largest for field-induced SIMs for cobalt(II) reported in the literature.

Taking advantage of “mild” preparation conditions we have been able for the first time to perform the synthesis of Ag₂S and luminescent AgInS₂ nanocrystals in an NMR tube.